1. Field of the Invention
The present invention relates to an image display projector for displaying an image formed by a reflective light valve such as a DMD onto a screen.
2. Description of the Related Art
In recent years, the DMD (Digital Micromirror Device: a trademark of Texas Instruments Incorporated) has attracted attention as a light valve used in the image display projector. The DMD electrically controls a plurality of 16xc3x9716 micron mirrors (hereinafter referred to as micromirrors) disposed on a silicon substrate, thereby controlling the reflection direction of light rays incident on micromirrors, each of which corresponds to a pixel. By tilting each micromirror +10 or xe2x88x9210 degrees, the incident light is separated into ON beams, which enters into a projection lens, and OFF beams blocked by a light absorber. The ON beams reflected by the micromirrors are projected through the projection lens and form an image onto a screen.
In conventional image display projectors using the DMD, a light generated by a light source is directed to the DMD surface using reflecting mirrors. These reflecting mirrors reflect the light to predetermined directions so as to introduce the light from the light source to the DMD surface. In such a structure, a prescribed spacing is required between the axis of the light emitted from the light source and the axis of the ON beams separated by the DMD, and so it is difficult to realize miniaturization of the projector.
As a solution to this problem, optical systems to miniaturize projecting device are disclosed in Japanese Patent Laid-Open No. 2000-98272 and Japanese Patent Laid-Open No. 2001-183603. In the disclosed projecting devices, a light from the light source is reflected by a first reflecting mirror, and the light reflected by this first mirror is reflected toward the DMD surface by a second reflecting mirror. Each optical element in the disclosed projecting devices is arranged so that the axis of the light emitted from the light source that enters into the first reflecting mirror becomes perpendicular to the axis of the ON beams separated by the DMD that enters into the projection lens. By introducing the light from the light source to the DMD in this manner, the axis of the light emitted from the light source and the axis of the ON beams can be placed close to each other, thereby reducing a size of the device.
Although the projecting devices cited above reallize miniaturization, they use a spherical or concave mirror for the second reflecting mirror, which is liable to cause aberration. Thus, angles of the light rays incident on each micromirror of the DMD become not uniform due to the aberration caused by the second reflecting mirror. Consequently, the ON beams and the OFF beams are not fully separated, and the contrast of the projected image decreases. Furthermore, because the directions of the ON beams reflected by the micromirrors also become not uniform, the quantity of the ON beams entering into a pupil of the projection lens decreases. Thus, the brightness of the image displayed on the screen deteriorates in the periphery.
This problem becomes more pronounced when the relative aperture of the second reflecting mirror is decreased to miniaturize the device.
The present invention is directed at solving these problems, and an object of the invention is to miniaturize the projector without causing contrast deterioration or uneven light intensity.
In one aspect of this invention, an image display projector includes a lens element for focusing a light beam from a lamp light source, a reflecting mirror for reflecting a light beam emitted from the lens element, an elliptical mirror for reflecting a light beam emitted from the reflecting mirror, a light valve for modulating a light beam reflected by the elliptical mirror, thereby forming an image light, and a projection lens for projecting the image light onto a screen. In this image display projector, a light focusing point, where the light beam emitted from the lens element is focused, is symmetric to one of the two focal points of the elliptical mirror with respect to the reflecting mirror, and the center of an entry pupil of the projection lens is symmetric to the second focal point of the elliptical mirror with respect to the light valve.
In another aspect of this invention, an image display projector includes a first lens element for focusing light from a lamp light source, a prismatic optical element, a second lens element for focusing a light from the prismatic optical element, a reflecting mirror for reflecting the light from the second lens element, an elliptical mirror for reflecting the light from the reflecting mirror, a light valve for modulating a light beam emitted from the elliptical mirror, thereby forming image light, and a projection lens for projecting the image light onto a screen. In the image display projector, a light focusing point, where the light beam emitted from the second lens element is focused, is symmetric to one of the two focal points of the elliptical mirror with respect to the reflecting mirror, and the center of an entry pupil of the projection lens is symmetric to the second focal point of the elliptical mirror with respect to the light valve.